When most people take a cruise they focus on the fun, the sun and the food. But here’s another thing to think about: sanitation. Poor sanitation can ruin your cruise. Just ask the 400-plus passengers and crew who were stricken by a suspected norovirus outbreak on a German cruise liner this week.

Transocean Tours’ ship the Marco Polo ended up terminating its scheduled 10-day voyage after only one sailing day in Ivergordon, Scotland. What’s the root cause for such an outbreak? It boils down to passenger health and the overall cleanliness of the ship.

Ship vigilance

The risk of contracting a contagious disease like norovirus illness is particularly high on a cruise ship because passengers mingle in a relatively confined space. For this reason, all cruise ships that dock in the United States and travel to foreign ports undergo regular inspections by the Centers for Disease Control and Prevention (CDC), Vessel Sanitation Program (VSP). Unfortunately for the Marco Polo’s passengers there is no European Union cruise ship inspection program like the CDC’s.

Cruise lines realize the best defense against viral and bacterial illnesses is constant vigilance, strict sanitation control and regular disinfection. And, they do a very good job at it. However, to keep them on their toes, the CDC conducts unannounced inspections of each ship twice a year. This cooperative effort is the chief reason there aren’t bigger outbreaks of illnesses at sea.

The CDC’s inspections are rigorous. Each inspection takes six to eight hours, depending on the size of the ship and the number of inspectors. The inspectors use a checklist to help evaluate such things as the ship’s water supply, food storage practices and food-preparation areas. Every ship starts with 100 points, then loses points for each infraction.

It doesn’t take much to lose points — anything from cracked tiles to refrigerators that aren’t quite cold enough. Inspection scores from the mid-80s to mid-90s are the most common. Ships scoring 86 points or higher are considered satisfactory; those scoring 85 and below are reinspected within 30 days.

All this inspecting is both reassuring and alarming, and wise travelers take their own precautions against picking up nasty germs at sea.

Sing to sanitation

Getting violently sick with an intestinal virus is a misery whether you’re on land or at sea. Seasoned travelers know all too well the importance of watching what they eat and washing their hands: It keeps the bugs at bay. Still, some of our fellow travelers aren’t so vigilant about hand washing, and they put us all at risk.

Poor hygiene spreads one of travelers’ worst enemies: noroviruses, also known as Norwalk virus and NLV, a group of viruses that can cause severe diarrhea, nausea and vomiting over a 48- to 60-hour period. The CDC estimates that 23 million people, or 8 percent of the U.S. population, develop symptoms of norovirus each year. Less than 1 percent of cruise passengers are affected by norovirus, but you don’t want to be one of them, do you?

So, remember what your mother told you: Wash your hands. For best results, says the CDC, moisten your hands with warm water before applying soap, then rub your hands together vigorously for at least 20 seconds — for as long as it takes to sing “Happy Birthday” twice. It is the soap combined with the scrubbing action that loosens and removes the germs from your hands. The CDC also says that hand sanitizing gels are not a substitute for hand washing, but they are helpful until you can wash your hands.

That’s all there is to it — 20 seconds of insurance that can literally save your health and your cruise.